1. Technical Field
Embodiments of the present invention generally relate to operation position sensor devices for electronic musical instruments which correctly detect operation positions of operation members, such as, keys of a keyboard device or the like.
2. Related Art
A key operation sensor device for a relatively inexpensive electronic musical instrument may detect key-depression speed of keys on the instrument by measuring a time difference in opening and closing between two or more switches provided on each of the keys. An electronic musical instrument in related art shown in FIG. 12 is provided with key switches each having a common member 103 and contacts 101 and 102, wherein key-depression speed is detected by measuring the time in which the common member 103 passes between the contacts 101 and 102.
A key operation sensor device for a relatively expensive electronic musical instrument may use various sensors to detect key depression speed and key depression force of keys on the instrument by measuring changes in pressure, magnetic force and the amount of reflection and transmission of light, which may occur in response to operations of the keys. For example, Japanese Laid-open Patent Application HEI 10-26983 (Patent Document 1) describes a sensor device having slits provided between a light emitting device and a photodetecting device. The slits are structured to continuously change the amount of light passing through the slits according to changes of the position of each key being operated, and the sensor device detects the position of the key operated based on the light detected by the photodetecting device. In the device described in Patent Document 1, two threshold light amounts are set corresponding to two key operation positions, and the key depression speed is obtained by measuring the time in which the amount of light detected by the photodetecting device passes these threshold light amounts.
Japanese Laid-open Patent Application SHO 63-81397 (Patent Document 2) describes a sensor device equipped with two pairs of light emitting elements and photodetecting element provided for each key at two operation positions of the key, and a shutter that is provided between the two pairs of light emitting element and photodetecting element and moves according to operations of the key. The sensor devices obtain the key depression speed by measuring the time in which the key passes the tow operation positions based on light detected by the respective photodetectors.
Japanese Laid-open Patent Application SHO 62-232572 (Patent Document 3) describes a sensor device shown in FIG. 13 and FIG. 14. The sensor device is equipped with a shutter 100 having two slits, a large slit a and a small slit b, attached to a key. The shutter 100 moves up and down upon depression of the key between a light emitting element 400 and a photodetecting element 500. The sensor device distinguishes the upper and lower slits by a difference in the amount of light passing through these two slits, detects the key depression position based on light detected by the photodetecting element 500, and detects the key depression speed by measuring the time in which the key passes two depression positions.
Japanese Laid-open Patent Application 2006-201704 (Patent Document 4) describes a sensor device equipped with two pairs (first pair and second pair) of light emitting element and photodetecting element provided in parallel with each other. A shutter that continuously changes the amount of transmission light according to changes in the position of a key being operated is provided between the light emitting element and photodetecting element in the first pair. Another shutter that transmits light only at two operation positions of the key is provided between the light emitting element and photodetecting element in the second pair. Based on the amount of light detected by the photodetecting element in the first pair at the time of detection of light by the photodetecting element in the second pair, the sensor device determines the relation between the amount of light detected by the photodetecting element in the first pair and the operation position of the key, and obtains the operation position of the key based on the amount of light detected by the photodetecting element in the first pair. In the sensor device described in Patent Document 4, light emitted from the light emitting element is guided through an optical fiber and a lens to the shutter, and the light that has passed through the shutter is guided through an optical fiber to the photodetecting element. Also, FIG. 2 of Patent Document 4 shows a state in which light emitted from the light emitting element is expanded by the lens placed on the side of the light emitting element into a parallel beam of light having a predetermined radius and guided to the shutter, and the parallel beam of light that has passed through the shutter is focused on the optical fiber on the light detecting side by the lens placed on the side of the photodetecting element.
In the case of the sensor system that uses opening and closing of switches, the key depression speed may not be accurately measured because the resilient force generated by the elasticity of the switches may act in excess on the keys more than necessary, and the contacts of the switches may wear out and deform after having been used for an extended period of time.
The method that detects changes in a continuous quantity such as light and magnetic is contactless and has no wear, but does not necessarily provide accurate measurement of position and speed of the key due to differences among the individual sensors, changes in the temperature and the like. In the sensor device described in Patent Document 1, the amount of light emission of light emitting elements and the photosensitivity of photodetecting elements may differ from one another among the individual elements, or the sensor device may be affected by changes in the ambient temperature, such that the key depression speed may be obtained at operation positions different from those intended by the designer. The sensor device described in Patent Document 2 can accurately obtain the timing at which the key passes two operation positions, but may have a complex structure because two pairs of light emitting elements and photodetecting elements need to be provided for each of the keys.
The sensor device described in Patent Document 3 provides some contrivances to minimize differences in the light emitting elements and the photodetecting elements and influences by temperature changes. However, as described below, the resolution of the positions of the slits is limited, such that the amount of transmitting light would become uncertain, which would generate error detections. Patent Document 3 shows changes in the amount of light passing through the slits which take place according to depression and release of the key, as shown in FIG. 15. As shown in the figure, a larger pulse b is generated after a smaller pulse a as the key is depressed. The time difference between the pulse a and the pulse b is measured, which is then converted to a key depression speed. Then, as the key is released, a larger pulse b is generated again and then a smaller pulse a occurs, and the key returns to the key's original state.
However, the light flux that has passed through the slit is spreading, such that the changes in the amount of light actually appear with its rising and falling being in continuous gentle hills and valleys due to dispersion, as shown in FIG. 16. With such an output of the photodetecting element, when the light flux relatively moves halfway in the larger slit b from its upper edge or lower edge, the change in the amount of light appears in a manner similar to a change that occurs when the light flux passes the smaller slit a. FIG. 17 shows the shutter 1 with its slits shown in enlargement, and FIG. 18 and FIG. 19 show movements of the photodetecting element 5 that moves relatively to the shatter 1. In FIG. 18, an upward arrow 1 on the far left side indicates that the key reaches the bottom dead point in full stroke, the next arrow 2 indicates that the photodetecting element 5 passes the slit b as the key returns, and the third arrow 3 indicates that the key is returning to the bottom dead point without going in a direction toward the initial position. The fourth arrow 4 indicates that the photodetecting element 5 returns from the middle of the hill to be presented by the slit b without passing its apex. The aforementioned movements cause changes in the amount of light as indicated by four pulses shown in FIG. 20 from the left side thereof, pulse a, pulse b, pulse b and pulse a. These changes are generally the same as the changes in the amount of light occurring when the key reaches the bottom dead point in full stroke, and then returns to the initial position, as shown in FIG. 16. Further, if the photodetecting element 5 hovers around the upper edge of the slit b as indicated by arrows 5, 6 and 7, the resultant pulse pattern becomes generally the same as the pattern to be generated when the key is depressed twice in succession, as indicated with successive pulses in FIG. 20. FIG. 19 shows an example of key movements in which the photodetecting element 5 relatively hovers near the upper edge of the slit b and moves to the apexes. Such movements are often generated by bouncing of the key or the hand of the performer. This problem is caused by the fact that the sensor output corresponding to the operation position is symmetrical through its apex due to the poor resolution of the slits and sensor.
The sensor device described in Patent Document 4 needs to be equipped with two pairs of light emitting elements and photodetecting elements for each of the keys and thus has a complex structure. Moreover, in the device described in Patent Document 4, neither the lens on the side of the light emitting element nor the lens on the side of the photodetecting element brings a focal point on the shutters, the light spot to be projected onto the shutter from the light emitting element is expanded to have a certain expansion, and light in the light spot having the certain expansion on the shutter is guided to the photodetecting element. Accordingly, even when the key is moved in a manner that the emitted light passes the shutter at a boundary portion where the amount of light transmission drastically changes from the maximum to the minimum or from the minimum to the maximum, the amount of light guided to the photodetecting element changes gently, which lowers the accuracy in detecting the key operation position, and makes it difficult to obtain an accurate operation position.
In the electronic musical instrument market, accurate and inexpensive operation position sensor devices with long serviceable life and excellent power of expression, which solve the problems described above, are demanded.